Attuatori SMA Adriano Basile STMicroelectronics, System LAB - - PowerPoint PPT Presentation

Elettronica e Controllo degli Attuatori SMA

Adriano Basile STMicroelectronics, System LAB

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STMicroelectronics: Who we are

Shape Memory Alloy Brief Mechanical Considerations SMA Driving Topology Experimental Results

• A global semiconductor leader
• The largest European semiconductor company
• 2012 revenues of $8.49B(1)
• Approx. 48,000 employees worldwide(1)
• Approx. 11,500(1) people working in R&D
• 12 manufacturing sites
• Listed on New York Stock Exchange, Euronext Paris

and Borsa Italiana, Milano

Who we are

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(1) Including ST-Ericsson

Partners with our Customers worldwide

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79 sales offices

in 35 countries

An unwavering Commitment to R&D

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(1) Including ST-Ericsson

Advanced research and development centers around the globe 16,000 patents; ~9,000 patent families; 515 new filings (in 2012) ~ 11,500(1) people working in R&D and product design

Digital Convergence Group (DCG) Imaging, BiCMOS, ASIC & Silicon Photonics (IBP) Automotive Product Group (APG) Analog, MEMS & Sensors (AMS) Microcontrollers, Memory & Secure MCU (MMS)

Embedded Processing Solutions (EPS)

Industrial & Power Discrete Group (IPD)

Product Segments

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Sense & Power and Automotive Products (SP&A)

Wireless (WPS)*

* former ST-Ericsson legacy products

Where you find us

7 Our automotive products are making driving safer, greener and more entertaining Our smart power products are making more of our energy resources Our MEMS & Sensors are augmenting the consumer experience Our Microcontrollers are everywhere making everything smarter and more secure Our digital consumer products are powering the augmented digital lifestyle

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STMicroelectronics: Who we are

Shape Memory Alloy Brief Mechanical Considerations SMA Driving Topology Experimental Results

Shape Memory Alloy (1/2)

• Shape memory alloys (SMA) form group of

metals that recovers particular shape when heated above their transformation temperatures.

• SMA deforms easily under stress, if such alloys

are plastically deformed at one temperature, they will completely recover their original shape on being raised to a higher temperature.

• The shape memory alloys have two stable

phases

• the high–temperature phase, called austenite
• the low–temperature phase, called martensite
• Shape memory alloys are also used in a wide

range of medical and dental applications (healing broken bones, misaligned teeth . . . )

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Solid-to-solid state transformation

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Shape Memory Alloy (2/2)

10 Diametro [μm] Forza massima [N] Contrazione Massima Forza suggerita [N] Contrazione suggerita 25 0,3 5% 0,1 3,5% 50 1,2 5% 0,3 3,5% 76 2,7 5% 0,8 3,5% 100 4,7 5% 1,3 3,5% 150 6,2 5% 2,7 3,5% 200 19 5% 5 3,5% 300 42 5% 12 3,5% 400 75 5% 21 3,5% 500 118 5% 33 3,5% 10

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STMicroelectronics: Who we are

Shape Memory Alloy Brief Mechanical Considerations SMA Driving Topology Experimental Results

Advantages for Linear Actuators

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Traditional Approach SMA Approach

Pro:

• The movement is really linear
• The system is silent
• The SMA wire does not occupy space

Con:

• One direction with one wire (a counter force is needed)

Further Mechanical Considerations

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Spring as counterforce

(no control)

Second Wire as counterforce

(fully controlled)

The Electronic has to satisfy both the approaches and…

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STMicroelectronics: Who we are

Shape Memory Alloy Brief Mechanical Considerations SMA Driving Topology Experimental Results

SMA Control Drv Topology

15 Diametro [μm] Forza massima [N] Contrazione Massima Forza suggerita [N] Contrazione suggerita 25 0,3 5% 0,1 3,5% 50 1,2 5% 0,3 3,5% 76 2,7 5% 0,8 3,5% 100 4,7 5% 1,3 3,5% 150 6,2 5% 2,7 3,5% 200 19 5% 5 3,5% 300 42 5% 12 3,5% 400 75 5% 21 3,5% 500 118 5% 33 3,5%

High Side Driving Low Side Driving

Current Generator

VDD

Shape Memory Alloy wire

Current Sink

VDD

Shape Memory Alloy wire

SMA Control Drv High Side Topology

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• MCU schedules and controls the main process routines:
• External Commands and Communication;
• SMA Actuators Current generators control;
• SMA data acquisition and elaboration;
• Offset management.

P-MOS Driver

Vdd

S/H

Offset

MCU

+ –

PGA V_SMA

Shape Memory Alloy wire

EXT INPUT

DAC ADC Driver

R_sense

SMA Control Drv Low Side Topology

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• MCU schedules and controls the main process routines:
• External Commands and Communication;
• SMA Actuators Current Sink control;
• SMA data acquisition and elaboration;
• Offset management.

N-MOS Driver

Vdd

S/H

Offset

MCU

+ –

PGA V_SMA

Shape Memory Alloy wire

EXT INPUT

DAC ADC

R_sense

Driver

Spec Example

18 Diametro [μm] Forza massima [N] Contrazione Massima Forza suggerita [N] Contrazione suggerita 76 2,7 5% 0,8 3,5%

P-MOS Driver Vdd S/H Offset

MCU

+ –

PGA V_SMA

Shape Memory Alloy wire

EXT INPUT

DAC ADC Driver R_sense

SMA Driving Waveform

• Current generator supplies measuring pulses @40mA
• Measurement required (typical) is Δ1Ω
• Voltage read with 12bit ADC (ref @2.5V)
• Measurement has to be amplified by gain factor = 31
• 40mA * Δ1Ω = Δ40mV
• Δ40mV*31= Δ1.240V
• 2.5V / 4096 = 0.6mV

Bill of Material from Spec

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Application Specific Integrated Circuit (ASIC)

Channel #1 Drive + Conditioning Stage Channel #2 Drive + Conditioning Stage Channel #4 Drive + Conditioning Stage Channel #3 Drive + Conditioning Stage USB conn Analog Conn. Reset PB Digital Conn. Analog Power Supply 6.5V Sens Digital Power Supply 5V MCU

Control Waveforms

• Each of the SMA wires is driven with a

control waveforms consisting of two phases:

• Ph1: measuring phase  40mA
• Ph2: driving phase, PWM mode  90mA
• During Ph2 driving signal is modulated

by varying the duty cycle of timers

• The target is to have a maximum of 2mW

when doing the measurement to keep the power delivered to the wire as low as possible

• The total resistance variation depend on

the wire length (i.e. 14mm may reach 6Ω)

• Generally the requested measurement

accuracy is 1mΩ / 1Ω. mW s s mA i R P 2 40 8 40 33

2 2

                

Measuring Phase Driving Phase Measuring Amplitude Measuring Phase (8μs) Driving Phase (32μs) Ton Driving Amplitude= 90mA 40mA

Ph1 Ph2

f=25 kHz

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Content

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STMicroelectronics: Who we are

Shape Memory Alloy Brief Mechanical Considerations SMA Driving Topology Experimental Results

Experimental Results

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First step has been emulate SMA wires and SMA based actuator with Matlab / Simulink

This has been obtained thanks to tri-lateral collaboration between ST, SAES Getter and Scuola Superiore S. Anna of Pisa

Experiments: Parameter Determination

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• Only a single wire is powered thus

allowing the resistance to leave the associated martensite (R0) value and progress along the SMA resistance curve. This test intends

• nly to follow only a part of the

resistance curve and not enter the austenite region.

• Procedure description
• Channel 2 is brought to R0 position, i.e.

Channel 1 is powered with a fixed duty cycle (≈17.3%) in order to straighten Channel 2 wire

• DAC for Channel 2 is set in order to output

~2V on the ADC.

• A 0.5Hz Saw tooth duty cycle (0% ÷ 10%)

waveform is fed on channel 2; measurement pulse only on the other channels RMAX

Time Resistance

Experiments: Hysteresis Curves (1/3)

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• Hysteresis curve Duty Cycle vs. Voltage is obtained
• The range of acquired voltage is [0:4095] ≡Δ2.5V
• With given amplification, considering Δ1Ω variation, the

range of output voltage is about 1.240V

• By performing consecutive acquisition with different DAC

values, the hysteresis curved is determined

• One wire is supplied with ramp waveform whose frequency

and max/min values are modified is several acquisitions

DC= DC_MIN DC= DC_MAX

Ch1

time DC =DC_MAX DC =DC_MIN

T=1/25KHz

time

Temperature

Experiments: Hysteresis Curves (2/3)

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• By increasing the frequency, the hysteresis curves results wider, time

is not enough for the wire to cool down

• opposite channel is power with opposite waveform in order to pull the hot wire

DC є [2:15]%, 1Hz DC є [2:20]%, 1Hz DC є [2:20]%, 2Hz DC є [2:20]%, 4Hz DC є [2:20]%, 8Hz

Duty Cycle V R

Experiments: Hysteresis Curves (3/3)

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• By modifying DAC value the whole hysteresis is exploited

Duty Cycle V R

DC= DC_MIN DC= DC_MAX

Ch1

time

Ch2

time V R DAC DAC variation

Experiments: Signal Follower

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• A sophisticated controller has been implemented in firmware, allowing

following results:

4 wires driven with ramp waveforms @20Hz, range [2000:3000]

Opposite channels Opposite channels

Experimental Results: live video

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Thank you!